A polyimide resin having high heat resistance, excellent electrical and mechanical properties and the like was conventionally used for a surface protection film or an interlayer insulating film of a semiconductor element. However, a resin of further improved performance has been lately required to satisfy the requirement for marked improvement in resistance against repeated heat or thermal shock due to higher integration and larger scale of a semiconductor element, thinning and down-sizing of a package, shift to surface mounting by reflow of solder and the like.
On the other hand, a technology to give photosensitivity to a polyimide resin itself has lately drawn attention, bringing about, for instance, a photosensitive polyimide resin represented by the formula (7) below. 
Using the above polyimide resin poses a problem in safety and handling due to necessity of spraying a solvent such as N-methyl-2-pyrrolidone in development, while a part of procedures to make a pattern can be simplified resulting in shorter process and improved yield. Therefore, a positive-working photosensitive resin that can be developed by an aqueous solution of an alkali has been lately exploited. For instance, a positive-working photosensitive resin comprising a polybenzoxazole precursor as a base polymer and a diazoquinone compound as a photosensitive material has been disclosed in JP-B-1-46862. This resin has high heat resistance, superior electrical properties and fine processability, and a potential of resin not only for wafer coating but also for interlayer insulation. With regard to a development mechanism of this positive-working photosensitive resin, a diazoquinone compound in an exposed area is subjected to a chemical change to become soluble in an aqueous solution of an alkali, while the diazoquinone compound in an unexposed area remains insoluble in the aqueous solution of the alkali. Utilizing the difference of solubility between the exposed area and the unexposed area, a pattern of coating film only in the unexposed area can be obtained by dissolving and removing the resin in the exposed area.
In an actual use of these photosensitive resins, sensitivity of the photosensitive resins is especially of significance. Low sensitivity requires a longer exposure time resulting in a lower throughput. On the other hand, if, for instance, a base polymer with a lower molecular weight is used in an attempt to improve sensitivity of a photosensitive resin, problems such as failing to obtain a desired film thickness or collapse of a pattern shape arise due to increased loss of film thickness in an unexposed area during development. Thus, development of a photosensitive resin of high sensitivity having such properties as described above has been greatly desired. In addition, since a thickness of resin film tends to increase from conventional about 5 to 7 μm to about 10 to 20 μm, a photosensitive resin with high sensitivity even in an increased thickness has been expected to be developed.